1. Field of the Invention
This invention relates to a microscope for observing the interior of the specimen of an organism, such as a living body, and the structure of an IC pattern configured on a semiconductor wafer and to an optical apparatus, such as an observation apparatus, using the microscope.
2. Description of Related Art
For the observation of fine structure inside a living body and the structural analysis of a semiconductor pattern, a microscope that has high resolution and a high sectioning effect is desired. As the microscope of this type, a confocal microscope has been used in which confocal pinholes are arranged at a position conjugate with an object to be observed. Two types of confocal microscopes are known. One of them is a laser scanning confocal microscope and the other is a Nipkow disk scanning confocal microscope. The laser scanning confocal microscope requires a relatively long scanning time to obtain an observation image of an object because the object is scanned with a laser beam. A confocal microscope improved to reduce this scanning time is the Nipkow disk scanning confocal microscope.
In the Nipkow disk scanning confocal microscope, however, confocal pinholes configured on the Nipkow disk must be spaced as far apart as possible in order to secure a sufficient confocal effect. This causes the problem of impairing the efficiency of utilization of light from a light source.
A confocal microscope designed to solve this problem of the Nipkow disk scanning confocal microscope is set forth in xe2x80x9cConfocal microscopy by aperture correlationxe2x80x9d, T. Wilson, R. Juskaitis, M. A. A. Neil, and M. Kozubek, OPTICS LETTERS, Vol. 21, No. 23, pp. 1879-1881. This confocal microscope is such that the confocal pinholes are arranged at random to thereby improve the efficiency of utilization of light from a light source, and consequent impairment in confocal effect is avoided by obtaining an image formed through randomly arranged pinholes and a bright-field image formed without using the pinholes to make a differential calculation relative to these images.
In recent years, research has been pursued on a technique of observing the structure of an object in which light is strongly scattered as in the interior of a living body. For such techniques, techniques based on optical coherence tomography are disclosed in many publications including Japanese Patent Preliminary Publication No. Hei 11-23372.
Apart from the optical coherence tomography, techniques of deriving only phase information from image information of objects are disclosed by the present inventor in Japanese Patent Preliminary Publication Nos. Hei 7-225341 and Hei 9-15504.
In particular, a differential interference contrast microscope (DIC microscope) set forth in Hei 9-15504 is used as a phase modulation DIC microscope and its effect is discussed in xe2x80x9cRetardation modulated differential interference microscope and its application to 3-D shape measurementxe2x80x9d, H. Ishiwata, M. Itoh, and T. Yatagai, Proc. SPIE, Vol. 2873, pp. 21-24 (1996).
A technique of using the laser scanning microscope to extract phase information is disclosed in Japanese Patent Preliminary Publication No. Hei 9-15503.
An example where the Nipkow disk scanning microscope is combined with the DIC microscope to realize a real-time confocal DIC microscope is disclosed in xe2x80x9cDifferential interference contrast imaging on a real time confocal scanning optical microscopexe2x80x9d, T. R. Corle and G. S. Kino, APPLIED OPTICS, Vol. 29, No. 26, pp. 3769-3774.
According to an observation technique disclosed in each of Hei 7-225341 and Hei 9-15504, only phase information can be extracted from the observation image of an object, and thus an image with high contrast can be obtained with respect to the sample of a living body or a semiconductor. Moreover, since the phase information is detected, a sectioning effect is better than that of a conventional microscope in which the intensity of light is detected.
By combining this technique with the Nipkow disk scanning confocal microscope, the contrast and the sectioning effect can be further improved. This is disclosed in xe2x80x9cDifferential interference contrast imaging on a real time confocal scanning optical microscopexe2x80x9d, T. R. Corle and G. S. Kino, APPLIED OPTICS, Vol. 29, No. 26, pp. 3769-3774. This publication, however, does not in any way suggest a solution for a problem relative to the efficiency of utilization of light from a light source in the Nipkow disk scanning confocal microscope.
By a combination of a phase detection technique disclosed in each of Hei 7-225341 and Hei 9-15504 and a confocal microscope described in xe2x80x9cConfocal microscopy by aperture correlationxe2x80x9d, T. Wilson, R. Juskaitis, M. A. A. Neil, and M. Kozubek, OPTICS LETTERS, Vol. 21, No. 23, pp. 1879-1881, the problem relative to the efficiency of utilization of light from a light source can be eliminated. However, the image formed through the randomly arranged pinholes and the bright-field image must be processed in a state where their phases are inverted, and four pieces of image information are required to obtain one confocal image. This gives rise to the problem of spending much time to obtain the confocal image.
The confocal microscope, although high in resolution and sectioning effect, is often used for a fluorescence observation by applying fluorescent pigment with respect to a method of observing an object with low reflectance, such as an organism specimen. This microscope is difficult to use a method of observing the object by light transmission or without using the fluorescent pigment, and thus this method is seldom used. As the reason for this, it is conceivable that light is strongly scattered inside the organism specimen.
In this respect, as mentioned above, when the optical coherence tomography disclosed, for example, in Hei 11-23372 is employed, it is possible to observe the interior of an object in which light is strongly scattered, such as the interior of a living body.
Even with the use of the optical coherence tomography, however, there are the problems that an optical system used does not form a common optical path and thus is subject to vibration, lateral resolution is low because an interferometer is used as it is, and an apparatus used is considerably large and becomes cumbersome.
It is, therefore, an object of the present invention to provide an optical apparatus and a microscope in which high resolution and sectioning effect are obtained and time required to obtain an output image is reduced.
It is another object of the present invention to provide an optical apparatus and a microscope in which the interior of an object that light is strongly scattered, such as the interior of a living body, can be observed without using fluorescent pigment and in which resistance to vibration is strong and observations can be carried out with high resolution.
It is still another object of the present invention to provide an optical apparatus and a microscope in which a lamination structure of an IC pattern configured on a semiconductor wafer, as well as the interior of a living body, can be observed.
In order to achieve these objects, according to one aspect of the present invention, the optical apparatus includes a light source; an illumination optical system for leading light emitted from the light source to an object to be observed; an imaging optical system for magnifying and projecting an image of the object; an aperture member which is rotatable, disposed at an image plane of the imaging optical system or its conjugate plane, and having an aperture section constructed with light-transmitting areas and light-blocking areas; a light-separating means for separating the light emitted from the light source into orthogonally polarized components; a light-combining means for combining the polarized components separated by the light-separating means, disposed in the imaging optical system; a polarized-light extracting means for deriving only a particular polarized component, interposed between the light-combining means and the image plane of the imaging optical system; an image sensor for picking up a magnified image of the object projected on the image plane of the imaging optical system; an image processor for storing an image obtained by the image sensor and using this image to perform a calculation; and a phase changer for changing a phase difference between the orthogonally polarized components, interposed between the light source and the light-separating means or between the light-combining means and the image sensor. The light-transmitting areas and the light-blocking areas of the aperture member have boundaries formed in the range from the vicinity of the center of rotation of the aperture member to the vicinity of the periphery thereof so that a differential image is formed by performing a differential calculation with respect to respective corresponding pixels from at least two differential interference contrast images in which the amounts of phase differences between their respective two polarized components are nearly the same, but have different signs.
According to another aspect of the present invention, the optical apparatus includes a light source; an illumination optical system for leading light emitted from the light source to an object to be observed; an imaging optical system for magnifying and projecting an image of the object; an aperture member which is rotatable, disposed at an image plane of the imaging optical system or its conjugate plane, and having an aperture section constructed with light-transmitting areas and light-blocking areas; a light-separating means for separating the light emitted from the light source into orthogonally polarized components; a light-combining means for combining the polarized components separated by the light-separating means, disposed in the imaging optical system; a polarized-light extracting means for deriving only a particular polarized component, interposed between the light-combining means and the image plane of the imaging optical system; an image sensor for picking up a magnified image of the object projected on the image plane of the imaging optical system; an image processor for storing an image obtained by the image sensor and using this image to perform a calculation; and a phase changer for changing a phase difference between the orthogonally polarized components, interposed between the light source and the light-separating means or between the light-combining means and the image sensor. The light-transmitting areas and the light-blocking areas of the aperture member have boundaries formed in the range from the vicinity of the center of rotation of the aperture member to the vicinity of the periphery thereof and boundaries shaped like concentric circles so that a differential image is formed by performing a differential calculation with respect to respective corresponding pixels from at least two differential interference contrast images in which the amounts of phase differences between their respective two polarized components are nearly the same, but have different signs.
The microscope according to the present invention includes a light source; an illumination optical system for leading light from the light source to an object to be observed; an imaging optical system for magnifying and projecting an image of the object; an aperture located at the pupil position of the illumination optical system; and a phase plate which is similar to an aperture, located at a position conjugate with the aperture placed in the illumination optical system through the object. The microscope further includes an aperture member comprised of a plurality of minute apertures whose positions are changed with time, placed at an image plane of the imaging optical system or its conjugate plane.